Network functions virtualization (NFV for short) is software processing for bearing many functions by using commodity hardware such as x86 and a virtualization technology, so as to reduce high device costs of a network. By means of software/hardware decoupling and function abstraction, a network device function no longer depends on special-purpose hardware, a resource can be fully and flexibly shared, a new service can be rapidly developed and deployed, and automatic deployment, auto scaling, fault isolation, self-healing, and the like are performed based on an actual service requirement. An NFV system is structured vertically and horizontally. According to an NFV design, there are three layers vertically: an infrastructure layer, a virtual network layer, and an operation support layer. There are two domains horizontally: a service network domain and a management and orchestration domain.
Because a telecommunications operator has a relatively high requirement on device reliability, generally, availability needs to reach five nines (that is, running interruption of a device is less than 5 minutes each year). In availability calculation, usually, an interruption time is manually and periodically counted, to determine whether a predetermined availability requirement is met. Specifically, availability may be calculated by using a system runtime and the interruption time. That is, Availability=(Runtime−Unavailable time)/Runtime. Because the runtime may be directly obtained by counting a time from a time point at which a device is powered on and starts running to a counting time point, a main issue is to count the unavailable time caused by a fault. In the prior art, during counting of the unavailable time, a third-party tool may be used to maintain a continuous connection, and whether a network is available is determined according to whether a service is available. The network is determined as unavailable when the third-party tool cannot connect to the network. This is often applied to an Internet network. Alternatively, when a fault occurs in the system, a maintenance engineer manually calculates an unavailable time of a service according to maintenance alarm information. This is often applied to a communications network. However, in the foregoing methods, only overall availability of a system (an Internet network or a communications device) is counted, and availability of different layers of a system, such as a network functions virtualization system, that includes a multilayer architecture cannot be determined.